Historic Preservation - Technical Procedures
Installing A New Bonded Terrazzo Floor To Match Historic Terrazzo
J.Weinberger Us Cthouse/San Diego, Ca - Hallenbeck, Chamorro
Installing A New Bonded Terrazzo Floor To Match Historic Terrazzo
INSTALLING A NEW BONDED TERRAZZO FLOOR TO MATCH HISTORIC TERRAZZO
A. This procedure includes guidance on installing new bonded
terrazzo to replace lost or severely damaged portions of
existing terrazzo floors, or to enlarge or alter an area
of existing/historic terrazzo floors. GENERALLY, THIS
WORK SHOULD BE ACCOMPLISHED BY A EXPERIENCED CONTRACTOR.
B. Characteristics of Terrazzo:
1. Good terrazzo has a smooth surface that is a
mixture of 70% or more coarse aggregate and 30% or
less portland cement matrix.
2. Terrazzo combines the durability of marble with the
strength and economy of concrete.
3. Ease of maintenance is one of the principal reasons
why terrazzo is found in so many buildings where
traffic is heavy.
4. Pre-cast terrazzo tiles may be available for
installation on all grade levels and over any sound
subfloor construction; Typical sizes are 8, 12, and
16 inches square.
C. See 01100-07-S for general project guidelines to be
reviewed along with this procedure. These guidelines
cover the following sections:
1. Safety Precautions
2. Historic Structures Precautions
4. Quality Assurance
5. Delivery, Storage and Handling
6. Project/Site Conditions
7. Sequencing and Scheduling
8. General Protection (Surface and Surrounding)
These guidelines should be reviewed prior to performing
this procedure and should be followed, when applicable,
along with recommendations from the Regional Historic
Preservation Officer (RHPO).
A. NTMA Standards: Comply with specified provisions and
recommendations of National Terrazzo and Mosaic
Association, Inc. (NTMA), 3166 Des Plaines Ave., Ste.
132, Des Plaines, IL 60018, 800/323-9736 or 708/635-
7744, FAX (708) 635-9127.
B. NTMA has materials and installation tips in their SWEET's
advertisement. Tips include:
1. Wax and sealant for required finish.
2. Abrasive strips added to finish at stairs, ramps,
A. Portland Cement: ASTM C150, Type I, except as modified
to comply with NTMA requirements for compressive
strength. Obtain cement from a single source for each
1. Provide non-staining white cement for terrazzo
B. Sand: ASTM C33
C. Water: Clean, free of oil, soluble salts or other
D. Aggregate: Natural, sound, crushed marble chips without
excessive flats or flakes, complying with NTMA
requirements. When matching existing terrazzo, the
original aggregate types and ratios are often found
listed on original drawings.
1. Colors and gradation of aggregate sizes as required
to match original existing intact materials and
2. Aggregate colors and matrix pigments should be
matched after cleaning or taken from the interior
of core samples depending upon scope of work.
E. Matrix Pigments: Pure mineral or synthetic pigments,
resistant to alkalies and non-fading. Mix pigments with
matrix to provide required colors.
F. Curing Compound: Liquid-membrane-forming compound, ASTM
C309, Type 1.
G. Divider Strips in new spaces (not requiring restoration):
Depth and style required for terrazzo type and thickness.
Divider strips should be of solid composition and match
existing (size, color, material). Materials may be
brass, zinc... Do not use coated divider strips.
1. CAUTION: Divider strips may be coated instead of
solid composition. Coated strips should not be
ground. Grinding may cause coated divider strips
to lose their coating and discolor.
2. NOTE: Use conventional terrazzo grinding equipment
rather than lighter type machines.
H. Accessory Strips: Match width, material and color of
divider strips, unless otherwise required. Provide
following types of accessory strips as required for
1. Control Joint Strips: Double or split units, 1/8"
wide, of same material and color as divider strips
with 1/8" wide full-depth filler, laminated between
I. Adhesive Bonding Agent: Epoxy or polyester resin.
A. Underbed: One part portland cement to 4-1/2 parts sand
and sufficient water to provide workability at as low a
slump as possible.
B. Terrazzo Topping: One 94 pound bag of portland cement as
per 200 pounds of marble chips and approximately 5
gallons of water.
1. Add color pigment as required to match existing
color. Do not exceed, however, 2 pounds of pigment
per bag of cement.
A. Examine the terrazzo to determine the type of terrazzo
topping used. Match marble chips and matrix for existing
terrazzo by size, mineral content and color. See
Submittals. Color samples should be taken after
B. Perform a thorough examination of the existing
conditions. Perform any necessary tests on an
inconspicuous surface to determine the current conditions
and appropriate steps and materials necessary for
replication and replacement of select areas of existing
A. Surface Preparation:
1. Clean and prepare substrate to comply with NTMA
specifications for type of terrazzo application
indicated. Clean substrate of loose chips and
foreign matter. Grind concrete substrate to
provide surfaces within tolerances required by NTMA
for type of terrazzo application.
2. For cementitious terrazzo, comply with NTMA
recommendations for proportioning mixes,
installation of strips, and for placing, curing,
grinding, grouting and finishing.
3. Thin-set Terrazzo:
a. Comply with NTMA guide specifications
previously referenced under "Thin-set Terrazzo
Materials" and with matrix manufacturer's
directions for installing and finishing thin-
set terrazzo. Match Contracting Officer's
sample and provide total material thickness
indicated. Sample should be taken after
cleaning or from core sample of existing
b. Exercise extreme care to ensure fluids from
grinding operation do not react with divider
or control joint strips to produce a stain on
aggregate or discolor strips.
c. Delay grinding and finishing until heavy trade
work is completed and construction traffic
through the area is restricted.
4. Provide terrazzo bases, thresholds, stair treads
and landings, without interruptions of seams,
except where divider strips, control joints and
expansion joints are required. Place and finish
terrazzo around obstructions to achieve continuous
color, pattern and finish.
5. Provide control joints where required by installing
angle-type divider strips back-to-back with
neoprene rubber filler cemented between strips,
flush with finish floor.
3.03 ERECTION, INSTALLATION AND APPLICATION
A. Match the historic character and pattern of the terrazzo
in all spaces containing or contiguous with existing
B. Sand Cushion (floating) Terrazzo: Comply with NTMA
"Guide Specification for Bonded Terrazzo".
1. Used where structural movement is anticipated from
settling, expansion, contraction, or vibration,
which may cause injury to the terrazzo topping;
2. The overall thickness of the underbed and topping
needs to be at least 3 inches.
3. The concrete slab is covered with a thin bed of dry
sand, over which is laid a waterproof membrane and
reinforcing wire mesh.
4. Install the terrazzo underbed to 5/8 inch below the
finished floor line.
5. Place divider strips and then pour terrazzo
C. Bonded-to-Concrete Terrazzo: Comply with NTMA "Guide
Specification for Bonded Terrazzo".
1. Used in all general areas-corridors, lobbies,
rooms, sidewalks, etc.
2. The minimum overall thickness (most common) is 1-
3/4 inches; With reinforcing, 2 or 2-1/2 inches is
3. Thoroughly clean and soak the base slab with water.
4. Slush it with dry portland cement to ensure a good
5. Install the underbed followed by the placing of
divider strips and terrazzo topping.
D. Monolithic Terrazzo: Installed at 5/8 inch thick, it is
bonded to or made integral with the prepared slab.
E. Thin Terrazzo Toppings: Installed at 3/8 inch thick on
concrete slab which has first been covered with adhesive
bonding agent, i.e., polysulfide liquid polymer.
1. Floor must be structurally sound and rigid.
2. Lay waterproof membrane such as 15-lb. roofing felt
or plastic sheeting.
3. Lay reinforcing wire mesh over membrane.
4. Spread 2" thick underbed of cement and sand.
5. Lay 5/8" topping.
G. Surfacing: Grout cured terrazzo topping in accordance
with NTMA specifications.
1. Delay grinding and finishing until heavy trade work
is completed and construction traffic through the
area is restricted.
2. Finish by fine grinding with abrasive grit of size
specified by NTMA, or as otherwise required to
match original intact material.
3. Grind and polish the new areas, patches, and the
entire floor as required to produce a clean,
smooth, and uniform finish, capable of being sealed
and polished to match the original installation.
NOTE: EXERCISE CAUTION WHEN GRINDING NEAR COATED
DIVIDER STRIPS (SEE 2.01 H.).
4. Cover with vapor barrier sheets to prevent quick
A. Keep terrazzo free of acids and oils.
B. Protect the floor, especially the grouting, with a
penetrating type seal.
C. Daily Cleaning:
1. Daily sweeping with a cotton-wick floor brush,
treated with a non-oily dressing, will control dust
and make maintenance easier.
2. Regular damp-mopping keeps the surface free from
D. Periodic Cleaning:
1. Machine buffing on a regular basis removes traffic
marks and restores luster.
2. Touching up with sealer in traffic areas as needed
protects the surface.
3. Periodic machine scrubbing removes heavy
accumulations of dirt.
4. Seal and wax as needed.
5. Use a penetrating type terrazzo seal.
6. Avoid seals which may turn yellow and discolor.
7. Normal stripping and buffing procedures are
C. Clean terrazzo after installation and finishing
operations are completed, complying with sealer
D. Apply sealer to cleaned terrazzo surfaces to comply with
sealer manufacturer's instructions.
E. Protect terrazzo from damage and wear during construction
END OF SECTION